How I get the cdata out in c function with variable arguments using luajit?

Question

Here is the code. The aim is to print messages. In PrintC, I would like to get e...but arrives as cdata. How can I unpack that or circumvent that?

extern "C"
{
    static int PrintC ( lua_State *L )
    {


         // does not work cdata
        //executor* e = ( executor* ) luaL_checkudata(L, 1, "cdata"); does n




        //luaL_checkudata(L, 1, "void *"); 

        if ( e->writelog )
        {
            int no = lua_gettop ( L ) ;

            for ( int i = 2; i <= no; i++ )
            {
                cout << lua_tostring (L,i);
            }


        }
        return 1;
    }

}

---

// initialised as
lua_pushcfunction ( L, PrintC );
lua_setglobal ( L, "PrintC" );
lua_pushinteger ( L, ( long ) this ); // this is in a class executor
lua_setglobal ( L, "p" );

---

p= ffi.cast("void *",p)
function   Print()
   return  PrintC(p)
end

Answer 1

You can't. The Lua C API and the LuaJIT FFI are deliberately separated and cannot interact.

Rewrite PrintC in Lua using the FFI, or write Lua C API bindings to the library you're using p with. I.e. Use one or the other.